计算机培训学习资料 cisco书籍OSPF

ConfiguringOSPF

IntroducingtheOSPFProtocol

Link-StateProtocols

SPFTree

•Neighbortable:

-Alsoknownastheadjacencydatabase

-Containslistofrecognizedneighbors

•Topologytable:

-TypicallyreferredtoasLSDB

-Containsallroutersandtheirattachedlinksintheareaor

network

-IdenticalLSDBforallrouterswithinanarea

•Routingtable:

-Commonlynamedaforwardingdatabase

-Containslistofbestpathstodestinations

Link-StateRoutingProtocols

•Link-stateroutersrecognizemoreinformationaboutthe

networkthantheirdistancevectorcounterparts.

•Eachrouterhasafullpictureofthetopology.

•Consequently,link-staterouterstendtomakemoreaccurate

decisions.

Link-StateDataStructure:

NetworkHierarchy

•Link-stateroutingrequiresahierachical

networkstructurethatisenforcedbyOSPF.

•Thistwo-levelhierarchyconsistsofthefollowing:

-Transitarea(backboneorarea0)

-Regularareas(nonbackboneareas)

OSPFAreas

OSPFarea

characteristics:BackboneArea0

•Minimizesrouting

tableentries

•Localizesimpactof

atopologychange

withinanarea

•DetailedLSA

floodingstopsat

theareaboundary

Area2Area3

•Requiresa0

0

^

hierarchicalAutonomousSystem8

networkdesign

AreaTerminology

•RoutersAandBare

backbonerouters.BackboneArea0

•Backbonerouters

makeuparea0.

•RoutersC,D,andEare

knownasareaborder

routers(ABRs).

•ABRsattachallother

areastoarea0.

Area2Area3

9

L9

g

AutonomousSystemm

OSPFAdjacencies

•Routersdiscoverneighborsbyexchanginghellopackets.

•Routersdeclareneighborstobeupafterchecking

certainparametersoroptionsinthehellopacket.

FormingOSPFAdjacencies

•Point-to-pointWANlinks:

-Bothneighborsbecomefullyadjacent.

•LANlinks:

-NeighborsformafulladjacencywiththeDRandBDR.

-Routersmaintaintwo-waystatewiththeotherrouters

(DROTHERs).

•Routingupdatesandtopologyinformationarepassedonly

betweenadjacentrouters.

•Onceanadjacencyisformed,LSDBsaresynchronizedby

exchangingLSAs.

•LSAsarefloodedreliablythroughoutthearea(ornetwork).

OSPFCalculation

Routersfindthebestpathstodestinationsby

applyingDijkstra'sSPFalgorithmtothelink-state

databaseasfollows:

•Everyrouterinanareahastheidentical

link-statedatabase.

•Eachrouterintheareaplacesitselfinto

therootofthetreethatisbuilt.

•Thebestpathiscalculatedwithrespecttothe

lowesttotalcostoflinkstoaspecificdestination.

•Bestroutesareputintotheforwardingdatabase(routing

table).

SPFCalculation

AdjacencyDatabaseForwardingDatabases

(Neighborsofx:A,B,C,D)(RoutingTable)oJ

AssumealllinksareEthernet,withanOSPFcostof10.

Link-StateDataStructures:LSAOperation

LSA

Send

LSAck

FloodLSASendLSUwith

newer

RunSPFtocalculateinformation

newroutingtabletosource

End

Summary

•Link-stateroutingprotocolsrespondquicklytochanges,

sendtriggeredupdateswhenchangesoccur,andsend

periodicupdatesevery30minutes.

•Atwo-tierhierarchicalnetworkstructureisusedbyOSPFin

whichthenetworkisdividedintoareas.Thisareastructureis

usedtoseparatetheLSDBintomoremanageablesizes.

•AdjacenciesarebuiltbyOSPFroutersusingtheHello

protocol.Overtheselogicaladjacencies,LSUsaresentto

exchangedatabaseinformationbetweenadjacentOSPF

routers.

Summary(Cont.)

•Dijkstra'sSPFalgorithmisusedtocalculatebestpathsfor

alldestinations.SPFisrunagainsttheLSDB,andthe

outcomeisatableofbestpaths,knownastheroutingtable.

•AfteranLSAentryages,therouterthatoriginatedtheentry

sendsanLSUaboutthenetworktoverifythatthelinkisstill

active.TheLSUcancontainoneormoreLSAs.

CiscoSYSTEMS

ConfiguringOSPF

OSPFPacketTypes

OSPFPacketTypes

❶Hello

2DatabaseDescription

3Link-StateRequest

7

❹Link-StateUpdate

■

5Link-StateAcknowledgmentri

OSPFPacketHeaderFormat

zzz

LinkIPOSPFLink

HeaderHeaderPacketTrailer

Types

Protocol

IDNumber

89=OSPF

Neighborship:TheHelloPacket

RouterID

Helloanddeadintervals*

Neighbors

AreaID*

Routerpriority

DRIPaddress

BDRIPaddress

Authenticationpassword*

Stubareaflag*

*Entrymustmatchonneighboringrouters

EstablishingBidirectionalCommunication

InitState

RouterB

NeighborsList

172.16.5.1/24,IntE1

IamrouterID172.16.5.2,andIsee172.16.5.1.

UnicasttoA◄----------------------------------------------------------------------------

RouterA

NeighborsList

172.16.5.2/24,IntEO

Two-V\^yState

DiscoveringtheNetworkRoutes

EO

172.16.5.1172.16.5.3

ExstartState

IwillstartexchangebecauseIhaverouterID172.16.5.1.

No,IwillstartexchangebecauseIhaveahigherrouterID.

◄---------------------------------------------------------------------------------------DBD

ExchangeState

HereisasummaryofmyLSDB.

HereisasummaryofmyLSDB.

DBD

AddingtheLink-StateEntries

Thanksfortheinformation!

LoadingState

Ineedthecompleteentryfornetwork172.16.6.0/24.

Hereistheentryfornetwork172.16.6.0/24.

Thanksfortheinformation!

—LSAck

FullState

MaintainingRoutingInformation

•RouterAnotifiesallOSPFDRson224.0.0.6.

•DRnotifiesotherson224.0.0.5.

LSASequenceNumbering

•EachLSAintheLSDBmaintainsasequencenumber.

•Thesequencenumberingschemeisa4-bytenumberthat

beginswith0x80000001andendswith0x7FFFFFFF.

•OSPFfloodseachLSAevery30minutestomaintainproper

databasesynchronization.EachtimetheLSAisflooded,the

sequencenumberisincrementedbyone.

•Ultimately,anLSAsequencenumberwillwraparoundto

0x80000001.Whenthisoccurs,theexistingLSAis

prematurelyagedtothemaximumage(onehour)and

flushed.

•WhenarouterencounterstwoinstancesofanLSA,itmust

determinewhichismorerecent.TheLSAhavingthenewer

(higher)LSasequencenumberismorerecent."

LSASequenceNumbersandMaximumAge

RTC#showipospfdatabase

OSPFRouterwithID(192.168.1.67)(ProcessID10)

RouterLinkStates(Area1)

LinkIDADVRouterAgeSeq#ChecksumLinkcount

192.168.1.67192.168.1.67480x800000080xB1122

192.168.2.130192.168.2.1302120x800000060x3F442

<outputomitted>

•EveryOSPFrouterannouncesarouterLSAforthose

interfacesthatitownsinthatarea.

•RouterwithlinkID192.168.1.67hasbeenupdatedeight

times;thelastupdatewas48secondsago.

debugipospfpacket

Debugofasinglepacket

Rl#debugipospfpacket

OSPFpacketdebuggingison

RI#

*Feb1611:03:51.206:OSPF:rev.v:2t:11:48rid:10.0.0.12

aid:0.0.0.1chk:D882aut:0auk:fromSerial0/0/0.2

•ShowsfieldsinOSPFheader

Summary

•TherearefiveOSPFpackettypes:hello,DBD,LSU,LSR,and

LSAck.

•TheHelloprotocolformslogicalneighboradjacency

relationships.ADRmayberequiredtocoordinateadjacency

formations.

•Theexchangeprotocolpassesthroughseveralstates

(down,init,two-way,exstart,andexchange)beforefinally

reachingthegoaloffullstate.Fullstatemeansthat

databasesaresynchronizedwithadjacentrouters.

Summary(Cont.)

•LSAsaresentonchangebutarealsosentevery30minutes

toensuredatabaseintegrity.ThemaximumtimethatanLSA

willstayinthedatabase,withoutanupdate,is1hour.The

LSAsequencenumberisincrementedeverytimeitis

advertised.

•EachLSAintheLSDBhasasequencenumber,whichis

incrementedbyoneeachtimetheLSAisflooded.Whena

routerencounterstwoinstancesofanLSA,itmustdetermine

whichismorerecent.TheLSAhavingthenewer(higher)LSA

sequencenumberismorerecent.

•UsethedebugipospfpacketcommandtoverifythatOSPF

packetsareflowingproperlybetweentworouters.

CiscoSYSTEMS

ConfiguringOSPF

ConfiguringOSPFRouting

ConfiguringBasicOSPF

Router(config)#

routerospfprocess-id[vrfvpn-name]

•EnablesoneormoreOSPFroutingprocesses

Router(config-router)#

networkip-addresswildcard-maskareaarea-id.

•DefinestheinterfacesthatOSPFwillrunon

Router(config-if)#

ipospfprocess-idareaarea-id[secondariesnone]

•OptionalmethodtoenableOSPFexplicitlyonaninterface

ConfiguringOSPFonInternalRoutersofa

SingleArea

BroadcastNetworkPoint-to-PointNetwork

<OutputOmitted><0utputOmitted>

interfaceFastEthernetO/OinterfaceFastEthernet0/0

ipaddress10.64.0.1255.255.255.0ipaddress10.64.0.2255.255.255.0

ff

<0utputOmitted>interfaceSerial0/0/l

routerospf1ipaddress10.2.1.2255.255.255.0

network10.0.0.00.255.255.255area0<OutputOmitted>

routerospf50

network10.2.1.20.0.0.0area0m

1network10.64.0.20.0.0.0area0

Li-----▽

Canassignnetworkor

interfaceaddress

ConfiguringOSPFforMultipleAreas

<outputomitted><outputomitted>

interfaceFastEthernetO/OinterfaceFastEthernet0/0

ipaddress10.64.0.1255.255.255.0ipaddress10.64.0.2255.255.255.0

<outputomitted>interfaceSerial0/0/l

routerospf1ipaddress10.2.1.2255.255.255.0

network10.0.0.00.255.255.255area0

ipospf50area1

<outputomitted>

routerospf509

g

o

id

network10.64.0.20.0.0.0area0n

co

OSPFRouterID

•TherouterisknowntoOSPFbytheOSPFrouterIDnumber.

•LSDBsusetheOSPFrouterIDtodifferentiateonerouterfromthe

next.

•Bydefault,therouterIDisthehighestIPaddressonanactive

interfaceatthemomentofOSPFprocessstartup.

•AloopbackinterfacecanoverridetheOSPFrouterID.Ifaloopback

interfaceexists,therouterIDisthehighestIPaddressonanyactive

loopbackinterface.

•TheOSPFrouter-idcommandcanbeusedtooverridetheOSPF

routerID.

•Usingaloopbackinterfaceorarouter-idcommandisrecommended

forstability.

LoopbackInterfaces

UnadvertisedloopbackaddressAdvertisedloopbackaddress

Ex.192.168.255.254Ex.172.16.17.5

•NotinOSPFtable•InOSPFtable

3

•Savesaddressspace•Usesaddressspace-

•Cannotusepingcommand•Canusepingcommand

Network

172.16.0.0

Router(config)#interfaceloopback0

Router(config-if)#ipaddress172.16.17.5255.255.255.255

•IftheOSPFprocessisalreadyrunning,theroutermustbe

reloadedortheOSPFprocessmustberemovedand

reconfiguredbeforethenewloopbackaddresswilltakeeffect.

OSPFrouter-idCommand

Router(config-router)#

router-idip-address

•Thiscommandisconfiguredundertherouterospf[process-id\

command.

•Anyuniquearbitrary32-bitvalueinanIPaddressformat

(dotteddecimal)canbeused.

•IfthiscommandisusedonanOSPFprocessthatisalready

active,thenthenewrouterIDisusedafterthenextreloador

manualOSPFprocessrestartusing:

Router#

clearipospfprocess

Router(config)#routerospf1

Router(config-router)#router-id172.16.1.1

Router#clearipospfprocess

OSPFRouterIDVerification

RouterB#shipospf

RoutingProcess"ospf50"withID10.64.0.2

<outputomitted>

Numberofareasinthisrouteris2.2normal0stub0nssa

Numberofareastransitcapableis0

Externalfloodlistlength0

AreaBACKBONE(0)

AreaBACKBONE(0)

Areahasnoauthentication

SPFalgorithmlastexecuted00:01:25.028ago

SPFalgorithmexecuted7times

<outputomitted>

Area1

Numberofinterfacesinthisareais1

Areahasnoauthentication

SPFalgorithmlastexecuted00:00:54.636ago

SPFalgorithmexecuted3times

<outputomitted>

VerifyingOSPFOperation

Router#

showipprotocols

•VerifiestheconfiguredIProutingprotocolprocesses,

parameters,andstatistics

Router#

showiprouteospf[process-id]

•DisplaysallOSPFrouteslearnedbytherouter

Router#

showipospfinterface[typenumber]

•DisplaystheOSPFrouterID,areaID,andadjacencyinformation

VerifyingOSPFOperation(Cont.)

Router#

showipospf

•DisplaystheOSPFrouterID,timers,andstatistics

Router#

showipospfneighbor[typenumber][neighbor-id]

[detail]

•DisplaysinformationabouttheOSPFneighbors,includingDR

andBDRinformationonbroadcastnetworks

Example:TheshowiprouteospfCommand

RouterA#showiprouteospf

10.0.0.0/8isvariablysubnetted,3subnets,2masks

OIA10.2.1.0/24[110/782]via10.64.0.2,00:03:05,FastEthernet0/0

RouterA#

Example:Theshowipospfinterface

Command

RouterA#showipospfinterfacefastEthernet0/0

FastEthernetO/Oisup,lineprotocolisup

InternetAddress10.64.0.1/24,Area0

ProcessID1,RouterID10.64.0.1,NetworkTypeBROADCAST,Cost:1

TransmitDelayis1sec,StateDROTHER,Priority0

DesignatedRouter(ID)10.64.0.2,Interfaceaddress10.64.0.2

Nobackupdesignatedrouteronthisnetwork

Timerintervalsconfigured,Hello10,Dead40,Wait40,Retransmit5

oob-resynctimeout40

Helloduein00:00:04

SupportsLink-localSignaling(LLS)

Index1/1,floodqueuelength0

Next0x0(0)/0x0(0)

Lastfloodscanlengthis1,maximumis4

Lastfloodscantimeis0msec,maximumis4msec

NeighborCountis1,Adjacentneighborcountis1

Adjacentwithneighbor10.64.0.2(DesignatedRouter)

Suppresshellofor0neighbor(s)

Example:Theshowipospfneighbor

Command

RouterB#showipospfneighbor

NeighborIDPriStateDeadTimeAddressInterface

10.64.0.10FULL/DROTHER00:00:3010.64.0.1FastEthernet0/0

10.2.1.10FULL/-00:00:3410.2.1.1Serial0/0/l

RouterB#showipospfneighbordetail

Neighbor10.64.0.1,interfaceaddress10.64.0.1

Inthearea0viainterfaceFastEthernet0/0

Neighborpriorityis0,StateisFULL,16statechanges

DRis10.64.0.2BDRis0.0.0.0

<outputomitted>

Neighbor10.2.1.1,interfaceaddress10.2.1.1

Inthearea1viainterfaceSerial0/0/l

Neighborpriorityis0,StateisFULL,6statechanges

DRis0.0.0.0BDRis0.0.0.0

<outputomitted>

Summary

•ConfigurationofOSPFisatwo-stepprocess:

-EnterOSPFconfigurationwiththerouterospfcommand.

-Usethenetworkcommandtodescribewhichinterfaceswill

runOSPFinwhicharea.

•OSPFselectsarouterIDatstartuptime:

-TherouterID9sspecifiedintherouter-idcommandunderthe

OSPFprocess.

-Otherwise,thehighestIPaddressofaloopbackinterface,if

thereareany,isused.

-Bydefault,thehighestIPaddressofallactiveinterfaces

•UsetheshowipospfcommandtoverifytherouterID.

•Usetheshowipprotocols,showiprouteospf,showipospf

interface,showipospf,andshowipospfneighborcommandsto

verifyOSPFoperation.

CiscoSYSTEMS

ConfiguringOSPF

OSPFNetworkTypes

OSPFNetworkTypes

ThethreetypesofnetworksdefinedbyOSPFare:

•Point-to-point:Anetworkthatjoinsasinglepairofrouters.

•Broadcast:Amultiaccessbroadcastnetwork,suchas

Ethernet.

•Nonbroadcastmultiaccess(alsocalledNBMA):Anetwork

thatinterconnectsmorethantworoutersbutthathasno

broadcastcapability.FrameRelay,ATM,andX.25are

examplesofNBMAnetworks.

一FivemodesofOSPFoperationareavailableforNBMA

networks.

Point-to-PointLinks

•UsuallyaserialinterfacerunningeitherPPPorHDLC.

•Mayalsobeapoint-to-pointsubinterfacerunningFrame

RelayorATM.

•NoDRorBDRelectionrequired.

•OSPFautodetectsthisinterfacetype.

•OSPFpacketsaresentusingmulticast224.0.0.5.

MultiaccessBroadcastNetwork

•Generallytheseare,LANtechnologieslikeEthernetand

TokenRing.

•DRandBDRselectionarerequired.

•AllneighborroutersformfulladjacencieswiththeDRand

BDRonly.

•PacketstotheDRandtheBDRuse224.0.0.6.

•PacketsfromDRtoallotherroutersuse224.0.0.5.

ElectingtheDRandBDR

•HellopacketsareexchangedviaIPmulticast.

•TherouterwiththehighestOSPFpriorityisselectedas

theDR.Therouterwiththesecond-highestpriorityvalueis

theBDR.

•UsetheOSPFrouterIDasthetiebreaker.

•TheDRelectionisnonpreemptive.

SettingPriorityforDRElection

Router(config-if)#

ipospfprioritynumber

•ThisinterfaceconfigurationcommandassignstheOSPF

prioritytoaninterface.

•Differentinterfacesonaroutermaybeassigneddifferent

values.

•Thedefaultpriorityis1.Therangeisfrom0to255.

•0meanstheroutercannotbetheDRorBDR.

•ArouterthatisnottheDRorBDRisDROTHER.

NBMATopology

•Asingleinterfaceinterconnectsmultiplesites.

•NBMAtopologiessupportmultiplerouters,butwithout

broadcastingcapabilities.

DRElectioninNBMATopology

•OSPFconsidersNBMAtobelikeotherbroadcastmedia.

•TheDRandBDRneedtohavefullymeshedconnectivitywith

allotherrouters,butNBMAnetworksarenotalwaysfully

meshed.

•TheDRandBDRneedalistofneighbors.

•OSPFneighborsarenotautomaticallydiscoveredbythe

router.

FrameRelayTopologies

Full-Mesh

Topology

£

StarTopology

(hub-and-spoke)

OSPFoverNBMATopologyModesof

Operation

•RFC2328-compliantmodesareasfollows:

-Nonbroadcast(NBMA)

-Point-to-multipoint

•AdditionalmodesfromCiscoareasfollows:

-Point-to-multipointnonbroadcast

-Broadcast

-Point-to-point

SelectingtheOSPFNetworkTypefor

NBMANetworks

Router(config-if)#

ipospfnetwork[{broadcast|non-broadcast|point-to-

multipoint[non-broadcast]|point-to-point}]

•DefinesOSPFnetworktype

Example:BroadcastMode

Router(config)#interfaceserial0/0/0

Router(config-if)#encapsulationframe-relay

Router(config-if)#ipospfnetworkbroadcast

NonbroadcastMode(NBMAMode)

•Treatedasabroadcast

networkbyOSPF

(actslikeaLAN).

•Allserialportsarepartof

thesameIPsubnet.

•FrameRelay,X.25,and

ATMnetworksdefaultto

nonbroadcastmode.

•Neighborsmustbe

staticallyconfigured.

•DuplicatesLSAupdates.

•ComplieswithRFC2328.

UsingtheneighborCommand

Router(config-router)#

neighborip-address[prioritynumber][poll-interval

number][costnumber][database-filterall]

•UsedtostaticallydefineneighborrelationshipsinanNBMA

network

neighborCommandExample

RouterA(config)#routerospf100

RouterA(config-router)#network192.168.0.00.0.255.255area0

RouterA(config-router)#neighbor192.168.1.2priority0

RouterA(config-router)#neighbor192.168.1.3priority0

RouterA(config-router)#network172.16.0.00.0.255.255area0

TheshowipospfneighborCommand

RouterA#showipospfneighbor

NeighborIDPriStateDeadTimeAddressInterface

192.168.1.30FULL/DROTHER00:01:57192.168.1.3Serial0/0/0

192.168.1.20FULL/DROTHER00:01:33192.168.1.2Serial0/0/0

172.16.1.11FULL/BDR00:00:34172.16.1.1FastEthernet0/0

Point-to-MultipointMode

•Thepoint-to-multipointmodeallowsforNBMAnetworking.

•Thepoint-to-multipointmodefixespartial-meshandstar

topologies.

•NoDRisrequiredandonlyasinglesubnetisused.

•A30-secondhelloisused.

•ThismodeisRFC2328-compliant.

Point-to-MultipointConfiguration

RouterA

interfaceSerial0/0/0

ipaddress192.168.1.1255.255.255.0

encapsulationframe-relay

ipospfnetworkpoint-to-multipoint

<outputomitted>

routerospf100

log-adjacency-changes

network172.16.0.00.0.255.255area0

network192.168.0.00.0.255.255area0

RouterC

interfaceSerial0/0/0

ipaddress192.168.1.3255.255.255.0

encapsulationframe-relay

ipospfnetworkpoint-to-multipoint

ipospfpriority0

Point-to-MultipointExample

RouterA#shipospfints0/0/0

Serial0/0/0isup,lineprotocolisup

InternetAddress192.168.1.1/24,Area0

ProcessID100,RouterID192.168.1.1,NetworkTypePOINT_TO_MULTIPOINT,

Cost:781

TransmitDelayis1sec,StatePOINT_TO_MULTIPOINT

Timerintervalsconfigured,Hello30,Dead120,Wait120,Retransmit5

oob-resynctimeout120

Helloduein00:00:26

SupportsLink-localSignaling(LLS)

Index2/2,floodqueuelength0

Next0x0(0)/0x0(0)

Lastfloodscanlengthis1,maximumis1

Lastfloodscantimeis0msec,maximumis4msec

NeighborCountis2,Adjacentneighborcountis2

Adjacentwithneighbor192.168.1.3

Adjacentwithneighbor192.168.1.2

Suppresshellofor0neighbor(s)

RouterA#

Point-to-MultipointNonbroadcast

•CiscoextensiontoRFC-compliantpoint-to-multipointmode

•Muststaticallydefineneighbors,likenonbroadcastmode

•Likepoint-to-multipointmode,DRandBDRnotelected

•Usedinspecialcaseswhereneighborscannotbeautomatically

discovered

UsingSubinterfaces

Router(config)#

interfaceserialnumber.subinterface-number{multipoint|

point-to-point}

•Thephysicalserialportbecomesmultiplelogicalports.

•EachsubinterfacerequiresanIPsubnet.

Router(config)#

interfaceserialnumber.subinterface-numberpoint-to-point

•EachPVCandSVCgetsitsownsubinterface.

•OSPFpoint-to-pointmodeisthedefaultonpoint-to-point

FrameRelaysubinterfaces.

-NoDR/BDR

一Donotneedtoconfigureneighbor